Test for filter with following content

The to_haml_filter method doesn’t properly tidy the end of the content
block, leaving extra whitespace that can cause following content to be
wrongly indented.

See #9
Fix trailing whitespace after filter content

Remove any trailing whitespace and replace with single newline so
following content is correctly indented.

Fixes #9
Add test for badly indented css/javascript

When a :javascript or :css filter is generated, if the first line is
indented further than any of the other lines, invalid Haml is produced.
Produce valid Haml for poorly indented filters

When a css or javascript filter is being generated, if the first line of
the code in the source is indented more than any other line then invalid
Haml is produced.

Fix this by simply stripping the leading whitespace away, and indenting
all lines by the current indentation amount. This may result in odd
looking output, but will at least be valid Haml.
Merge pull request #22 from haml/filter-trailing-whitespace

Filter trailing whitespace